11: Dick Costolo

STAGE OF GLOBAL CONQUEST: A leadership shake-up, competition from Facebook, and an indecently exposed congressman haven’t slowed Twitter down. The company now has more than 200 million registered users, and 200 million tweets are sent every day.

EVIDENCE OF POSSIBLY MACHIAVELLIAN BEHAVIOR: When Costolo joined the company as chief operating officer in 2009, he posted an ominous message on his personal Twitter page: “Task #1: undermine CEO, consolidate power.” The tweet was a joke, but it was also prescient. Last October, C.E.O. Evan Williams turned the company over to Costolo, and in June co-founder Biz Stone announced that he too was leaving.

UNFORESEEN CONSEQUENCES: The reputation of Twitter blossomed during the Arab Spring, as real-time tweets helped galvanize the revolution. August’s London riots, however, exposed a darker side, as looters used the service to gloat over their unlawful behavior.